Posted by **stefanie** on Sunday, May 2, 2010 at 11:43am.

2. The new Twinkle bulb has a standard deviation hours. A random sample of 77 light bulbs is selected from inventory. The sample mean was found to be 492 hours.

a. Find the margin of error E for a 90% confidence interval.

Round your answer to the nearest hundredths.

- statistics -
**MathGuru**, Sunday, May 2, 2010 at 6:15pm
Margin of error = z-value (sd/√n)

Find the z-value corresponding to 90% confidence using a z-table.

sd = standard deviation

n = sample size

I hope this will help get you started.

- statistics -
**Anonymous**, Tuesday, June 1, 2010 at 11:54am
Please someone help me? The new twinkle bulb has a standard deviation 35 hours. A random sample of 50 light bulbs is selected from inventory. The sample mean was found to be x=500 hrs. Find the margin of error for 95%, construct a 95% confidence interval for the mean life of all Twinkle bulbs. I am desperate.

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